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	/*
	* Copyright (c) 2008, 2021, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.nio.fs;

	import java.nio.file.ClosedWatchServiceException;
	import java.nio.file.DirectoryIteratorException;
	import java.nio.file.DirectoryStream;
	import java.nio.file.Files;
	import java.nio.file.LinkOption;
	import java.nio.file.NotDirectoryException;
	import java.nio.file.Path;
	import java.nio.file.StandardWatchEventKinds;
	import java.nio.file.WatchEvent;
	import java.nio.file.WatchKey;
	import java.nio.file.attribute.BasicFileAttributes;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.security.PrivilegedExceptionAction;
	import java.security.PrivilegedActionException;
	import java.io.IOException;
	import java.util.HashMap;
	import java.util.HashSet;
	import java.util.Iterator;
	import java.util.Map;
	import java.util.Set;
	import java.util.concurrent.Executors;
	import java.util.concurrent.ScheduledExecutorService;
	import java.util.concurrent.ScheduledFuture;
	import java.util.concurrent.ThreadFactory;
	import java.util.concurrent.TimeUnit;

	/**
	* Simple WatchService implementation that uses periodic tasks to poll
	* registered directories for changes. This implementation is for use on
	* operating systems that do not have native file change notification support.
	*/

	class PollingWatchService
	extends AbstractWatchService
	{
	// map of registrations
	private final Map<Object, PollingWatchKey> map = new HashMap<>();

	// used to execute the periodic tasks that poll for changes
	private final ScheduledExecutorService scheduledExecutor;

	PollingWatchService() {
	// TBD: Make the number of threads configurable
	scheduledExecutor = Executors
	.newSingleThreadScheduledExecutor(new ThreadFactory() {
	@Override
	public Thread newThread(Runnable r) {
	Thread t = new Thread(null, r, "FileSystemWatcher", 0, false);
	t.setDaemon(true);
	return t;
	}});
	}

	/**
	* Register the given file with this watch service
	*/
	@SuppressWarnings("removal")
	@Override
	WatchKey register(final Path path,
	WatchEvent.Kind<?>[] events,
	WatchEvent.Modifier... modifiers)
	throws IOException
	{
	// check events - CCE will be thrown if there are invalid elements
	final Set<WatchEvent.Kind<?>> eventSet = new HashSet<>(events.length);
	for (WatchEvent.Kind<?> event: events) {
	// standard events
	if (event == StandardWatchEventKinds.ENTRY_CREATE \|\|
	event == StandardWatchEventKinds.ENTRY_MODIFY \|\|
	event == StandardWatchEventKinds.ENTRY_DELETE)
	{
	eventSet.add(event);
	continue;
	}

	// OVERFLOW is ignored
	if (event == StandardWatchEventKinds.OVERFLOW) {
	continue;
	}

	// null/unsupported
	if (event == null)
	throw new NullPointerException("An element in event set is 'null'");
	throw new UnsupportedOperationException(event.name());
	}
	if (eventSet.isEmpty())
	throw new IllegalArgumentException("No events to register");

	// Extended modifiers may be used to specify the sensitivity level
	int sensitivity = 10;
	if (modifiers.length > 0) {
	for (WatchEvent.Modifier modifier: modifiers) {
	if (modifier == null)
	throw new NullPointerException();

	if (ExtendedOptions.SENSITIVITY_HIGH.matches(modifier)) {
	sensitivity = ExtendedOptions.SENSITIVITY_HIGH.parameter();
	} else if (ExtendedOptions.SENSITIVITY_MEDIUM.matches(modifier)) {
	sensitivity = ExtendedOptions.SENSITIVITY_MEDIUM.parameter();
	} else if (ExtendedOptions.SENSITIVITY_LOW.matches(modifier)) {
	sensitivity = ExtendedOptions.SENSITIVITY_LOW.parameter();
	} else {
	throw new UnsupportedOperationException("Modifier not supported");
	}
	}
	}

	// check if watch service is closed
	if (!isOpen())
	throw new ClosedWatchServiceException();

	// registration is done in privileged block as it requires the
	// attributes of the entries in the directory.
	try {
	int value = sensitivity;
	return AccessController.doPrivileged(
	new PrivilegedExceptionAction<PollingWatchKey>() {
	@Override
	public PollingWatchKey run() throws IOException {
	return doPrivilegedRegister(path, eventSet, value);
	}
	});
	} catch (PrivilegedActionException pae) {
	Throwable cause = pae.getCause();
	if (cause instanceof IOException ioe)
	throw ioe;
	throw new AssertionError(pae);
	}
	}

	// registers directory returning a new key if not already registered or
	// existing key if already registered
	private PollingWatchKey doPrivilegedRegister(Path path,
	Set<? extends WatchEvent.Kind<?>> events,
	int sensitivityInSeconds)
	throws IOException
	{
	// check file is a directory and get its file key if possible
	BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class);
	if (!attrs.isDirectory()) {
	throw new NotDirectoryException(path.toString());
	}
	Object fileKey = attrs.fileKey();
	if (fileKey == null)
	throw new AssertionError("File keys must be supported");

	// grab close lock to ensure that watch service cannot be closed
	synchronized (closeLock()) {
	if (!isOpen())
	throw new ClosedWatchServiceException();

	PollingWatchKey watchKey;
	synchronized (map) {
	watchKey = map.get(fileKey);
	if (watchKey == null) {
	// new registration
	watchKey = new PollingWatchKey(path, this, fileKey);
	map.put(fileKey, watchKey);
	} else {
	// update to existing registration
	watchKey.disable();
	}
	}
	watchKey.enable(events, sensitivityInSeconds);
	return watchKey;
	}

	}

	@SuppressWarnings("removal")
	@Override
	void implClose() throws IOException {
	synchronized (map) {
	for (Map.Entry<Object, PollingWatchKey> entry: map.entrySet()) {
	PollingWatchKey watchKey = entry.getValue();
	watchKey.disable();
	watchKey.invalidate();
	}
	map.clear();
	}
	AccessController.doPrivileged(new PrivilegedAction<Void>() {
	@Override
	public Void run() {
	scheduledExecutor.shutdown();
	return null;
	}
	});
	}

	/**
	* Entry in directory cache to record file last-modified-time and tick-count
	*/
	private static class CacheEntry {
	private long lastModified;
	private int lastTickCount;

	CacheEntry(long lastModified, int lastTickCount) {
	this.lastModified = lastModified;
	this.lastTickCount = lastTickCount;
	}

	int lastTickCount() {
	return lastTickCount;
	}

	long lastModified() {
	return lastModified;
	}

	void update(long lastModified, int tickCount) {
	this.lastModified = lastModified;
	this.lastTickCount = tickCount;
	}
	}

	/**
	* WatchKey implementation that encapsulates a map of the entries of the
	* entries in the directory. Polling the key causes it to re-scan the
	* directory and queue keys when entries are added, modified, or deleted.
	*/
	private class PollingWatchKey extends AbstractWatchKey {
	private final Object fileKey;

	// current event set
	private Set<? extends WatchEvent.Kind<?>> events;

	// the result of the periodic task that causes this key to be polled
	private ScheduledFuture<?> poller;

	// indicates if the key is valid
	private volatile boolean valid;

	// used to detect files that have been deleted
	private int tickCount;

	// map of entries in directory
	private Map<Path,CacheEntry> entries;

	PollingWatchKey(Path dir, PollingWatchService watcher, Object fileKey)
	throws IOException
	{
	super(dir, watcher);
	this.fileKey = fileKey;
	this.valid = true;
	this.tickCount = 0;
	this.entries = new HashMap<Path,CacheEntry>();

	// get the initial entries in the directory
	try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
	for (Path entry: stream) {
	// don't follow links
	long lastModified =
	Files.getLastModifiedTime(entry, LinkOption.NOFOLLOW_LINKS).toMillis();
	entries.put(entry.getFileName(), new CacheEntry(lastModified, tickCount));
	}
	} catch (DirectoryIteratorException e) {
	throw e.getCause();
	}
	}

	Object fileKey() {
	return fileKey;
	}

	@Override
	public boolean isValid() {
	return valid;
	}

	void invalidate() {
	valid = false;
	}

	// enables periodic polling
	void enable(Set<? extends WatchEvent.Kind<?>> events, long period) {
	synchronized (this) {
	// update the events
	this.events = events;

	// create the periodic task
	Runnable thunk = new Runnable() { public void run() { poll(); }};
	this.poller = scheduledExecutor
	.scheduleAtFixedRate(thunk, period, period, TimeUnit.SECONDS);
	}
	}

	// disables periodic polling
	void disable() {
	synchronized (this) {
	if (poller != null)
	poller.cancel(false);
	}
	}

	@Override
	public void cancel() {
	valid = false;
	synchronized (map) {
	map.remove(fileKey());
	}
	disable();
	}

	/**
	* Polls the directory to detect for new files, modified files, or
	* deleted files.
	*/
	synchronized void poll() {
	if (!valid) {
	return;
	}

	// update tick
	tickCount++;

	// open directory
	DirectoryStream<Path> stream = null;
	try {
	stream = Files.newDirectoryStream(watchable());
	} catch (IOException x) {
	// directory is no longer accessible so cancel key
	cancel();
	signal();
	return;
	}

	// iterate over all entries in directory
	try {
	for (Path entry: stream) {
	long lastModified = 0L;
	try {
	lastModified =
	Files.getLastModifiedTime(entry, LinkOption.NOFOLLOW_LINKS).toMillis();
	} catch (IOException x) {
	// unable to get attributes of entry. If file has just
	// been deleted then we'll report it as deleted on the
	// next poll
	continue;
	}

	// lookup cache
	CacheEntry e = entries.get(entry.getFileName());
	if (e == null) {
	// new file found
	entries.put(entry.getFileName(),
	new CacheEntry(lastModified, tickCount));

	// queue ENTRY_CREATE if event enabled
	if (events.contains(StandardWatchEventKinds.ENTRY_CREATE)) {
	signalEvent(StandardWatchEventKinds.ENTRY_CREATE, entry.getFileName());
	continue;
	} else {
	// if ENTRY_CREATE is not enabled and ENTRY_MODIFY is
	// enabled then queue event to avoid missing out on
	// modifications to the file immediately after it is
	// created.
	if (events.contains(StandardWatchEventKinds.ENTRY_MODIFY)) {
	signalEvent(StandardWatchEventKinds.ENTRY_MODIFY, entry.getFileName());
	}
	}
	continue;
	}

	// check if file has changed
	if (e.lastModified != lastModified) {
	if (events.contains(StandardWatchEventKinds.ENTRY_MODIFY)) {
	signalEvent(StandardWatchEventKinds.ENTRY_MODIFY,
	entry.getFileName());
	}
	}
	// entry in cache so update poll time
	e.update(lastModified, tickCount);

	}
	} catch (DirectoryIteratorException e) {
	// ignore for now; if the directory is no longer accessible
	// then the key will be cancelled on the next poll
	} finally {

	// close directory stream
	try {
	stream.close();
	} catch (IOException x) {
	// ignore
	}
	}

	// iterate over cache to detect entries that have been deleted
	Iterator<Map.Entry<Path,CacheEntry>> i = entries.entrySet().iterator();
	while (i.hasNext()) {
	Map.Entry<Path,CacheEntry> mapEntry = i.next();
	CacheEntry entry = mapEntry.getValue();
	if (entry.lastTickCount() != tickCount) {
	Path name = mapEntry.getKey();
	// remove from map and queue delete event (if enabled)
	i.remove();
	if (events.contains(StandardWatchEventKinds.ENTRY_DELETE)) {
	signalEvent(StandardWatchEventKinds.ENTRY_DELETE, name);
	}
	}
	}
	}
	}
	}

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